Toy balloons generally have an inflated diameter ranging from about 15 cm to about 50 cm. These are conventionally filled with helium gas. Such lighter than air balloons have been widely sold and used for a number of years at places like circuses, fairs, toy stores, and the like. Another common use for such balloons is for advertising purposes wherein a logo or advertising message is printed on the outside surface of the balloon. In more recent years there has been a proliferation of balloon greeting service companies who, for a fee, deliver bunches of helium inflated elastomeric balloons, usually conveying a personal message, to individuals on birthdays, anniversaries, Valentine's Day, or other special occasions. Another popular use for this balloon delivery service is to send a get well message with up to a dozen helium inflated balloons to an adult or child who is convalescing from an illness in a hospital or other institution.
A major problem with such prior art helium filled elastomeric balloons is that they do not remain buoyant for very long; their typical buoyant lifetime ranges from a few hours to a day or so. This short buoyant lifetime is due to the diffusion of the very small helium atoms through the elastomeric envelope provided by the balloon. Because of the short buoyant lifetime, such balloons must be inflated at the time of sale or just prior to sale. They cannot be inflated in advance and stocked for use when needed.
Burchett U.S. Pat. No. 4,634,395, the disclosure of which is incorporated herein by reference, discloses a method of increasing the floating life of helium filled elastomeric balloons by coating a surface of the balloon with a solution of polyvinyl alcohol and a water soluble plasticizer such as glycerine which is the best known and most frequently used plasticizer for polyvinyl alcohol. Burchett also recited a group of other water soluble plasticizers which included ethylene glycol, propylene glycol, butylene glycol, sorbitol, diglycerol, low molecular weight polyethylene glycols, ethanolamine salts, sodium or ammonium thiocyanate, ethanol acetamide and ethanol formamide.
It was found that although the polyvinyl alcohol water solution alone would give increased floating life, the balloons underwent an undesirable change in appearance on aging. Namely, these balloons developed surface wrinkles within a day or two after inflation with helium and the wrinkling became progressively worse on aging the inflated balloons. After five or six days the balloons were severely puckered and disfigured. This wrinkling was aesthetically objectionable and also made writing on the balloons illegible. The wrinkling characteristics could be greatly reduced or eliminated by adding up to 20 percent by weight of a water soluble plasticizer for polyvinyl alcohol to the solution. However, the addition of water soluble plasticizer was found to decrease the buoyant lifetime of the balloon compared to the use of unplasticized polyvinyl alcohol.
Therefore the optimum concentration of plasticizer was found to be one that was just sufficient to eliminate wrinkling of the balloon. While several plasticizers were found to be useful, glycerine was found to be very effective at preventing wrinkling at concentrations low enough to still give a major increase in buoyant lifetime.
One disadvantage of such coatings taught by Burchett is that at high relative humidity, the overall buoyant lifetime of the coated balloon decreases significantly. For example, helium filled balloons coated with the coating solution disclosed in Burchett which floated an average of 10 days at 40 percent relative humidity were found to float only 6 days at 80 percent humidity and only 4 days at 90 percent humidity. This problem of increased permeability with increasing humidity is made worse by the glycerine plasticizer which acts as a humectant.